A microphone preamplifier is a device used to increase the level of the microphone signal (typically by millivolts) to values close to the line level. Although it is assumed that these devices are intended to serve as a low-frequency (LF) amplifier, their imperfections are often used in the process of creating sound. They can also be part of a larger whole, i.e. a microphone track (stand-alone or being part of the mixer) containing additional signal processors like noise gates, filters, compressor, DeEsser, parametric EQ, limiter.
In terms of the applied signal enhancer elements the following are distinguished:                Tube preamplifiers        Transistor preamplifiers        Discrete        Based on operational amplifiers        
Usually preamplifiers work in class A because of the required low level of harmonic distortion and relatively low power consumption. Due to the nature of the load strengthening voltage rather than power is sought. Typical maximum gain value of the voltage range from 50 to 70 dB. In addition, a switched muffler is often installed on the input of the device, reducing the value of the signal in the event of a high level (condenser microphone signals can reach up to a few volts). A signal phase inverter, AC symmetrical voltage ±48 V (i.e. Phantom power) for condenser microphones and high-pass filter are other frequently encountered additional elements.
The present invention relates to a low-frequency voltage amplifier (LF) designed to work with a graphene microphone, inter alia. The intended use is to increase the level of received acoustic signal at the output of a graphene microphone with the amplitude of millivolts to values close to the line level. Moreover, as everyone knows each element of the acoustic route and the way preamplifiers and power systems are designed have an impact on the nature of sound quality driving in fact the power amplifier. The type and quality of the components used to build audio tracks (especially microphone preamplifiers) have a significant impact on the nature and quality of the sound, as for an amplifier according to the invention minimal impact on the change in the nature of the reproduced audio signal from the microphone was achieved.
Publication US 20100322440 A1 discloses an audio signal processing circuit derived from a microphone, which comprises two symmetrical preamplifier and amplifier paths. This solution allows to obtain a higher quality signal by comparing the two differential output signals, but the end result still leaves much to be desired because of the sensitivity of the circuit to the quality of elements used, and the frequent use of inferior components on account of their price.
Also US 2014153746 A1 discloses a preamplifier, dedicated to cooperation with the microphone. The solution allows a significant reduction in the space occupied by the circuit in the printed circuit board and to reduce power consumption by the preamplifier. It does not solve the problem of significant sensitivity of the circuit to the quality of the components used.
In the light of these solutions it can be seen that there are no preamplifiers dedicated to cooperate with the microphones that provide high quality of the processed signals, even when using less expensive components.